Boiler structure and method of assembly

ABSTRACT

A support structure for a boiler envelope, for example being the boiler envelope of a boiler thermal plant, a boiler structure so supported, and a method of supporting a boiler, are described. The support structure includes a support platform structure, comprising a part of the primary load bearing boiler cold structure for the boiler envelope, and adapted to engage with and thereby carry at least a major part of the static load of the boiler envelope. The support platform structure is provided surroundingly about the boiler envelope at a support platform level substantially below full envelope height and provided with associated further boiler cold structure in such manner that at least the substantial majority of the boiler cold structure is at or below the support platform level and preferably such that essentially all the boiler cold structure is at or below the support platform level and only elements of the boiler hot structure and the boiler pressure parts extend above the support platform level supported by the boiler cold structure.

The invention relates to a boiler structure, for example for a thermal power generation plant, and in particular to a support structure for a boiler envelope and to a boiler apparatus incorporating such a support structure. The invention further relates to a method of assembly of a boiler structure and in particular a method of assembly of a support structure for a boiler envelope and of a boiler envelope supported by such a support structure.

Thermal power plant driven by combustion of carbonaceous fuel for the generation of steam within a boiler system (which term as used herein encompasses subcritical and supercritical systems) remains a major source of generation of electrical power. Large scale boiler systems, especially fuelled by combustion of carbonaceous fuel, also have other industrial applications.

Boiler systems for a thermal power plant or other industrial apparatus on a comparable scale are large and complex apparatus requiring complex assembly and extensive structure. Although small industrial boilers, for example up to around 30 MW generating capacity, may practically be self-supporting, larger boilers, for example utility boilers of 60 MW generating capacity and above, typically require extensive supporting structures. In particular, extensive support structures are required to provide a mechanical support for and structural stability to the boiler envelope. Such structures are necessary to carry the high static mechanical loads associated with the boiler envelope and to transmit those loads to the ground, and also to provide stability and to accommodate operational load factors, such as those which might be attributable to thermal expansion effects and environmental influences such as weather and seismic influences on the large boiler envelope structures. Such support structures can be expensive both in terms of the structural materials used and in terms of the build complexity. Support structures for the boiler envelope can have a very large footprint.

In a typical prior art construction, a boiler house is first constructed including a large primary support structure which incorporates as part of the primary support structure a suspension deck in the vicinity of the boiler house roof and above the boiler envelope maximum height. The boiler envelope and associated structures are then supported on the primary suspension deck by suitable secondary and tertiary structural elements. The primary load carrying structure for the entire boiler envelope, including the heating surfaces within the boiler envelope and the boiler envelope structural elements themselves, is primarily supported via the suspension deck, and the associated load primarily transmitted to the ground via the suspension deck and associated supporting primary structure.

As the skilled person will understand, it is conventional in the art to consider the elements of a boiler envelope and support structure to fall into one of three classifications: boiler pressure parts; boiler hot structures; and boiler cold structures. In particular it is conventional to classify the structural support elements into boiler hot structures and boiler cold structures. The distinction will be well understood by the skilled person but can perhaps be expressed simply by defining boiler hot structures as those support structures which are designed to expand and contract thermally with the boiler, and boiler cold structures as those support structures which do not.

In the typical prior art construction above described the suspension deck comprises a generally horizontally extending primary support structure which sits at full height above the maximum height of the boiler envelope in the boiler house roof. Typically, the whole boiler house primary structure goes up to the level of this full height suspension deck, and supports the suspension deck at roof height to complete the primary load bearing structure. Thus, in the typical design, the boiler cold structures extend to a full height above the maximum height of the boiler envelope whereby the boiler hot structures and thereby the boiler pressure parts are supported.

Such an arrangement produces a boiler cold structure with a large footprint extending fully above the height of the boiler envelope and extensively beyond the boiler envelope footprint and requires a large quantity of high strength structural steel to make up the extensive full height boiler cold structure.

Moreover such an arrangement typically requires the boiler house, and in particular at least the boiler cold structure including the suspension deck, to be constructed in its entirety first, before any boiler envelope structure, heating surfaces etc can be brought into position and supported upon it. The prior art support system does not lend itself to progressive parallel construction from the ground upwards.

The invention is directed at providing a support structure for a boiler envelope and a method of assembly of a boiler support structure which mitigate some or all of the above disadvantages.

In a particular preferred case the invention is directed at the provision of a support structure for a boiler envelope which offers simplicity of fabrication and/or a reduction in the structural material requirement and/or a reduction in the overall structural envelope.

In a particular preferred case the invention is directed at a method of assembling the support structure which facilitates the progressive parallel construction of the support structure and of a supported boiler envelope.

Thus, in accordance with the invention in a first aspect a support structure for a boiler envelope, for example being the boiler envelope of a boiler thermal plant, comprises:

a support platform structure, comprising a part of the primary load bearing boiler cold structure for the boiler envelope, and adapted to engage with and thereby carry at least a major part of the static load of the boiler envelope;

wherein the support platform structure is provided surroundingly about the boiler envelope at a support platform level substantially below full envelope height and provided with associated further boiler cold structure in such manner that at least the major part and preferably substantially all of the boiler cold structure is at or below the support platform level.

That is to say in the alternative, in accordance with the invention in a first aspect a support structure for a boiler envelope, for example being the boiler envelope of a boiler thermal plant, comprises:

a boiler support cold structure including a support platform structure and a boiler support hot structure supported via the boiler support cold structure;

wherein the support platform structure is provided surroundingly about the boiler envelope at a support platform level substantially below full envelope height and configured such that at least the major part and preferably substantially all of the boiler cold structure is at or below the support platform level.

The support platform structure of the invention is in broad structural terms the equivalent to the primary load bearing structure provided in the prior art by the full height suspension deck. The support platform structure of the invention performs an equivalent mechanical function. It is a primary loaded bearing structure to carry at least a static load of the boiler envelope. It is a primary load bearing part of the boiler cold structure by means of which the boiler hot structures and thereby the boiler pressure parts are supported.

However the support platform structure of the invention can be contrasted with a prior art suspension deck at roof height, above the entire boiler structure, in that it eliminates the need for boiler cold structure above the support platform level. At least the substantial majority and preferably essentially all the boiler cold structure is at or below the support platform level, and only elements of the boiler hot structure and the boiler pressure parts extend above the support platform level supported by the boiler cold structure.

Advantages can accrue over a prior art design with boiler cold structure including a suspension deck which sits at full height above the maximum height of the boiler envelope in the boiler house roof in two ways in particular. First, the boiler cold structure of the present invention is all at substantially below full height. Second, in consequence, whereas the prior art cold structure extends across and over the boiler envelope footprint, in the present invention that the support platform structure surrounds the boiler envelope, the boiler envelope passing through it via an apertured portion. This can reduce the overall footprint. Both of these may produce a significant reduction in the overall structural requirement, and in particular in the requirement for higher strength structural materials.

The Invention further provides as an advantage that the boiler envelop may expand thermally upward and downward from the support platform structure, providing a qualitative change to the way boiler is supported and expanded, adding core value to the design by removal of much of the variable and constant spring requirements that are found in prior art designs.

The support platform structure performs otherwise a similar role, within the boiler cold support structure, as the prior art suspension deck structure, and aspects of the of the support platform structure of the invention may consequently be inferred from the prior art by analogy. In particular, the support platform structure of the invention preferably comprises a substantially horizontal framework of structural members, for example structural steel members, extending around and supporting the boiler envelope at the desired height substantially below the boiler maximum height. The support platform structure forms part of the primary load bearing boiler cold structure which boiler cold structure will include vertical structural elements which support the boiler hot structure and transmit the primary load directly from the support platform structure to the ground in familiar manner. Suitable secondary and tertiary structural elements, including suitable cross members, beams, ties, buckstays, tensile members and the like as applicable will complete the load transmitting structure in a manner which will be generally familiar to the skilled engineer.

In accordance with the invention, the support platform structure is provided at a height level substantially below the full height of the boiler envelope and there is preferably essentially no cold structure above this height. In a particular preferred case the support platform structure is provided at a height above the burners (and typically for example above any overfire airports if present, and typically for example just below or level with any cage ring main if present) but below the heating surfaces (and typically therefore below the soot blowers etc.). In a typical boiler design embodying the principles of the invention a preferred support platform structure level will be at around 40 to 60 per cent of the boiler envelope maximum height, and this level may be referred herein below for convenience as “half height”. However, the skilled person will appreciate that the principles set out above are the ones that are important for determining an ideal location in conjunction with the particular boiler structure to which the support structure of the invention is to be associated.

The invention takes advantage of the fact that in typical burner design a significant majority of the equipment within the boiler house is below the half height level. By providing a primary support platform structure at this level it may be possible to substantially reduce or eliminate the requirement for any boiler cold structure at all above this level. The support platform structure performs a similar role, within the boiler cold structure, as the prior art suspension deck structure, and as a result a full height suspension deck structure and associated boiler cold structure comparable with that in the prior art is not required. It is not necessarily for the boiler cold structure to extend to the full boiler house height and to the full extent of the footprint, as is required in the prior art. The extent of the boiler cold structure can be reduced in terms of height and/or footprint, with a potential for simplification of construction and for reduction in the quantity of structural steel requirement. Both of these can confer significant savings. It is possible to dispense with boiler cold structure altogether above the level of the suspension deck structure, relying only on boiler hot structural elements above this level.

A further potential advantage of the support structure in accordance with the invention may accrue in relation to flexibility of construction. If, in accordance with the invention, the boiler cold structure extends only up to the half height support platform structure, it ceases to be necessary to construct the boiler house and all of the associated full height structural support elements before considering assembly of the boiler envelope and associated structures. It is possible to construct and support the boiler assembly on the half height suspension deck and through the aperture therein, and to develop a method of assembly of a support structure and boiler envelope in integrated manner which is at least to some extent progressively effected. It is not necessary to build support structures to full height of the suspension deck structure before commencing assembly of the boiler envelope, but merely to the half height of the support platform structure. It is necessary only to complete that part of the support platform structure and associated cold structure and hot structure that directly bears on the boiler envelope structure before beginning construction of the side walls. The structure that is required before parallel construction of the boiler can start may be relatively much reduced. The roof can be built as a separate module away from the site. This parallel construction option may confer significantly increased flexibility in practice.

In the preferred case, a support platform structure in accordance with the invention is provided at a support platform level generally above the burners but below the heating surface of a typical boiler structure. All the boiler cold structure is at or below the support platform level. Only elements of the boiler hot structure and the boiler pressure parts extend above the support platform level supported by the boiler cold structure. In a typical boiler structure to which the support structure of the invention is intended to be applied, the majority of associated functional components within the boiler house will similarly be below this level, including for example the secondary air duct and other secondary structures. There are some functional structures above this level, notably including the heating surfaces and other boiler envelope structures, soot blowers and the like which may require some support structure to transmit residual static loads and to stabilise against dynamic load variations, in particular, for example against lateral movement, but the structural requirement above the half height level is substantially reduced. Any such additional support structure need extend only across the horizontal extent of the boiler envelope/hot structures not to the full extent of the boiler house to full height as is the case with prior art designs. For both these reasons, there will be a significant reduction in the structural material requirement above the half height support platform structure. In particular, there is no requirement for a full height suspension deck as such, as the primary static load bearing role it performs in the prior art boiler cold structure is at least in major part performed in the invention by the half height support platform structure.

The invention does not preclude the provision of support structure elements above the height of the primary support platform structure, and in particular considers that structural elements forming part of the boiler hot structure may be provided above this height, for example to stabilise/support the envelope/heating surfaces above mid height and/or accommodate expansion, stabilise the structure laterally against environmental dynamic loads etc. However, the invention is characterised in that it substantially eliminates the need for boiler cold structure above the primary support platform structure level.

Regardless of such provision of boiler hot structure above the support platform structure level the general principle of the invention is maintained, in which an integrated structure is provided which seeks to take the boiler cold structure down to half height. The skilled person will readily appreciate that the limited hot structure which may optionally be provided above this support platform structure level is not in engineering terms in any way equivalent to the full height suspension deck and associated boiler cold structure in the prior art.

Additional lateral stabilisation may be provided as required in a familiar manner.

In a particular preferred case, additional structural elements associated with the support structure of the invention may include buckstay arrangements such as are described in International Publication WO2010/0730030.

In accordance with a more complete aspect of the invention, a boiler apparatus comprises a support structure as hereinbefore described in conjunction with and providing at least a major part of the static load support for a boiler envelope, in particular of a boiler apparatus comprising part of a thermal power generation plant.

In particular the boiler is a utility boiler for thermal power generation on a utility scale, for example with 60 MW generating capacity and above. Such boilers in the prior art typically have boiler cold structures which in conventional design extend to and beyond the full boiler envelope height and have a large footprint. The invention when applied to such boilers offers significant constructional advantages as above described.

In a further more complete embodiment, a thermal power generation plant includes at least one such boiler apparatus.

In accordance with the invention the further aspect, a method of assembly of a boiler apparatus comprises the steps of:

providing a support structure for a boiler envelope in accordance with the above described first aspect of the invention;

assembling a boiler envelope so as to be mechanically supported thereon in such a manner that at least the major part and preferably substantially all of the boiler cold structure is at or below the support platform level and there is essentially no boiler cold structure above the support platform level; that is, only elements of the boiler hot structure and the boiler pressure parts extend above the support platform level supported by the boiler cold structure.

The invention further comprises by analogy a method of assembly of provision of a thermal power generation plant including at least one such boiler apparatus.

As has been previously noted, it is a particular preferred feature of the support structure in accordance with the invention, and in particular of the fact that the full height suspension deck and associated boiler cold structure is dispensed with, and instead a boiler cold structure at less than full height is provided which includes a support platform apertured to surroundingly support the boiler envelope, that it lends itself to parallel assembly of supporting structure and boiler envelope structure.

Thus, in a preferred embodiment of the method, the steps of providing a support structure, and assembling in a supporting manner thereon a boiler envelope structure, are performed progressively in parallel. This can be contrasted with typical prior art methods, where it is necessary to assemble the entire support structure, and indeed the entire boiler house, before suspension of the boiler envelope from the primary suspension deck structure can be commenced.

The invention will now be described by way of example only with reference to the accompanying drawings in which:

FIG. 1 is a schematic side view in elevation of a typical prior art thermal power plant boiler and support structure;

FIG. 2 is a schematic side view in elevation of an embodiment of support structure in accordance with the invention as applied to a boiler such as that in FIG. 1;

FIG. 3 is a plan view of the support structure of FIG. 2 at primary support platform structure level;

FIG. 4 is a plan view of the support structure of FIG. 2 at roof level;

FIG. 5 is a more detailed end elevation of the framework structure below support platform structure level;

FIG. 6 is a sectional view of a possible embodiment by means of which thermal expansion and contraction may be accommodated by the roof indicating movement of walls, buckstays, roof, heating surface supports and galleries when the roof is designed to move upwards when the wall expands horizontally and vertically.

FIG. 1 is a representation of a typical boiler structure to which a support structure in accordance with the invention might be applied, but shown in the case of FIG. 1 in side elevation with a prior art supporting structure including a conventional suspension deck. It will be appreciated that this is an example only of a boiler structure which the invention might be applicable, and that the invention might confer advantages to any boiler structure with similar structural considerations. It will also be appreciated that where example dimensions for the structures of FIG. 1 and FIG. 2 are given herein, they are for exemplification only.

FIG. 1 illustrates a typical vertical boiler assembly with a typical prior art primary support structure with the boiler cold structure extending to full height and supporting the boiler hot structure and pressure parts from above maximum boiler envelope height. For simplicity, most structural elements other than primary structural elements have been omitted.

The primary structure consists of a primary boiler support structure 1 and a SCR support structure 3. The boiler support structure consists of a suspension deck 5 at approximately 15 metres above the boiler roof level. In the example embodiment, the suspension deck is thus at approximately 82 metres above the ground. The suspension deck 5 forms the main load bearing part of the boiler cold structure. The boiler hot structure and thereby the envelope and the heating surfaces are all supported from this deck via slings 7.

The deck typically consist of several very large structural steel beams, usually around 5 metres to 6 metres deep depending on boiler width and on loads spanning across the boiler lateral plain. Interconnecting beams, designed as secondary structure and laid out in boiler fore and aft directions, are arranged to suit the sling positions.

With this arrangement, the boiler vertical expansion is entirely downward from the roof. The boiler framing designed to restrain the boiler envelope in the horizontal plane is supported by the boiler envelope.

As can be seen from the figure, the primary structural framework making up the boiler cold structure extends to the full extent of the boiler house and to the full height of the suspension deck 5 at 82 metres.

The boiler cold structure as a result has a substantial footprint, and requires primary structural elements to the full height of the boiler house. This imposes a significant structural steel requirement. Estimated structural steel requirements for the typical prior art design illustrated in FIG. 1 are in excess of 11,000 tonnes.

A side elevation of a modified support structure embodying the principles of the invention, employed in association with an equivalent boiler to that shown in FIG. 1, is presented in FIG. 2.

In FIG. 2, the full height primary structure suspension deck is dispensed with. Instead, the primary support platform 15 is provided at mid height, above the burners 17 but below the heating surfaces 19. This carries a substantial part of the static load of the boiler envelope and associated structures.

In the embodiment, the boiler support platform is provided at a 42 metre level, and the boiler cold support structure associated with the boiler support platform, and required to transmit the load from the boiler support platform to the ground, consequently only needs to rise to this 42 metre level, rather than, as in FIG. 1, to the full height and full extent of the boiler house at the 83 metre level. This eliminates the need for boiler cold structure above the 42 metre level. All the boiler cold structure is at or below the 42 metre level. Only elements of the boiler hot structure and the boiler pressure parts extend above the 42 metre level supported by the boiler cold structure.

Secondary supporting structure 21 is provided above the 42 metre platform level. All horizontal forces above this supporting platform level are transmitted to the boiler envelope via braces and tie bars, and then transmitted to the structure below support level by appropriate links. The wall lateral stiffness is maintained by a buckstay system, such as described in International Patent Publication WO2010/073030.

In the embodiment, boiler hot structural elements and a roof structure 23 are shown at 75 metre level. Alternatively, at least the boiler envelope may be self-supporting above the 42 metre level. However, it will be appreciated even in the embodiment where boiler hot structural elements and a roof structure 23 are present that this is in engineering terms a very different structure from the suspension deck 5 and associated cold structure in the prior art illustration of FIG. 1. None of the structure above the 42 metre level is cold structure. Only elements of the boiler hot structure and the boiler pressure parts extend above the 42 metre level. There is a substantial saving, both in terms of footprint and in terms of material requirement, above the platform level of 42 metres. In the proposed design, the structural steel requirement may be reduced to below 8000 tonnes. This is because the boiler cold structure has both reduced footprint and reduced height, and the structural steel requirement above the 42 metre platform level is substantially reduced.

FIG. 3 illustrates the 42 metre level platform structure in more detail in plan view, and in particular illustrates the manner in which it surroundingly supports the boiler envelope. Even at this level, the design allows for a reduction in footprint.

FIG. 4 illustrates in plan view the roof level support at 75 metres, and shows the much reduced footprint and structural requirement at this level when a half height support platform structure 15 and associated boiler cold structure at or below this height is provided in accordance with the invention.

FIG. 5 illustrates in end elevation the open frame primary structural support arrangement by which load is transmitted from the support platform 15 at the 42 metre level to the ground. The use of cross bracings 35 in addition to conventional horizontal and vertical framework elements opens up the framework below the platform level, providing at its widest opening of 21.5 metres. This can be contrasted by the conventional framework structure in FIG. 1 which has a maximum dimension of 12 or 13 metres. This open framework, together with the requirement to construct the primary support platform only to the half height 42 metre level, combined to facilitate the simultaneous progressive assembly of the support structure and the boiler envelope. It is only necessary to develop the support structure up to platform level to the extent sufficient to support the boiler side walls before it becomes possible to begin to assemble the boiler envelope within, through and upwardly from the aperture defined by the 42 metre platform support. The possibility of jacking from below rather than below using large cranes from above may further simplify the assembly process.

FIG. 6 illustrates a possible embodiment by means of which thermal expansion and contraction may be accommodated by incorporating the roof into the boiler hot structure. The figure illustrates movement of walls, vertical buckstays, gallery and roof due to boiler expansion.

With reference to FIG. 6, the increase in wall temperature will result in boiler wall expansion outward. In the embodiment an assumed expansion is in the y direction (i.e. a boiler lateral direction) and the magnitude is 63 mm and assuming that the wall is supported at 42000 mm level and free to expand upward (as well as downward) from this level. It follows that when the wall expand horizontally outwards, the wall and the roof intersection will tend to expand upward by 140 mm and the central part of the roof will need to move upward by the same amount if the stress level at the roof and the heating surface is to be negligible.

In the illustrated embodiment this is enabled by supporting the roof and the heating surface by angulated links L4 and L5. The diagram indicates the link cold positions marked by C which will move to their corresponding hot positions marked by H when the vertical buckstay is moved outward by 63 mm as a result of boiler expansion. This is controlled by the movement of horizontal buckstays such as for example are described in International Patent Publication WO2010/073030 incorporated herein by reference. The diagram also indicates two spring units marked as S1 and S2. However it is noted that the system will work with other arrangements for example using other link systems. The system further indicates gallery support and other structure which are integral part of the total system.

Thus, the design in accordance with FIGS. 2 to 6 represents a potentially significant improvement over the prior art design in FIG. 1. There is a potential reduction in structural weight, and an associated cost reduction, of around 30 per cent when compared to conventional support structures having substantial boiler cold structure to full height. Parallel construction may be enhanced leading to a significant reduction in construction lead time. The overall footprint of the boiler may be reduced. 

1. A support structure for a boiler envelope, for example being the boiler envelope of a boiler thermal plant, comprising: a support platform structure, comprising a part of the primary load bearing boiler cold structure for the boiler envelope, and adapted to engage with and thereby carry at least a major part of the static load of the boiler envelope; wherein the support platform structure is provided surroundingly about the boiler envelope at a support platform level substantially below full envelope height and provided with associated further boiler cold structure in such manner that at least the substantial majority of the boiler cold structure is at or below the support platform level.
 2. A support structure in accordance with claim 1 comprising: a boiler support cold structure including a support platform structure and a boiler support hot structure supported via the boiler support cold structure; wherein the support platform structure is provided surroundingly about the boiler envelope at a support platform level substantially below full envelope height and configured such that at least the substantial majority of the boiler cold structure is at or below the support platform level.
 3. A support structure in accordance with claim 1 wherein essentially all the boiler cold structure is at or below the support platform level and only elements of the boiler hot structure and the boiler pressure parts extend above the support platform level supported by the boiler cold structure.
 4. A support structure in accordance with claim 1 wherein the support platform structure comprises a substantially horizontal framework of structural members extending around and supporting the boiler envelope at a height substantially below the boiler maximum height.
 5. A support structure in accordance with claim 1 further comprising suitable secondary and tertiary structural elements, including suitable cross members, beams, ties, buckstays, tensile members and the like.
 6. A support structure in accordance with claim 1 wherein the support platform structure is provided in association with a boiler at a height above the burners of the boiler but below the heating surfaces of the boiler.
 7. A support structure in accordance with claim 1 wherein the support platform structure is provided in association with a boiler such that all the boiler cold structure sits at or below a maximum height level which maximum height level is above the burners of the boiler but below the heating surfaces of the boiler.
 8. A support structure in accordance with claim 1 wherein the support platform structure is provided in association with a boiler at a height of around 40 to 60 per cent of a boiler envelope maximum height.
 9. A support structure in accordance with claim 1 wherein the support platform structure is provided in association with a boiler such that all the boiler cold structure sits at or below a maximum height level which maximum height level is around 40 to 60 per cent of a boiler envelope maximum height.
 10. A boiler apparatus comprising a support structure in accordance with claim 1 in conjunction with and providing at least a major part of the static load support for a boiler envelope of a boiler.
 11. A boiler apparatus in accordance with claim 10 wherein the boiler is a utility boiler for thermal power generation.
 12. A thermal power generation plant including at least one boiler apparatus in accordance with claim
 10. 13. A method of assembly of a boiler structure comprising the steps of: providing a support structure for a boiler envelope in accordance with the above described first aspect of the invention; assembling a boiler envelope so as to be mechanically supported thereon in such a manner that at least the major part and preferably substantially all of the boiler cold structure is at or below the support platform level.
 14. The method of claim 13 wherein the boiler envelope is supported such that there is essentially no boiler cold structure above the support platform level and essentially only elements of the boiler hot structure and the boiler pressure parts extend above the support platform level.
 15. The method of claim 13 wherein the steps of providing a support structure, and assembling in a supporting manner thereon a boiler envelope structure, are performed progressively in parallel. 